Medical devices are used to treat patients suffering from a variety of ailments and symptoms. Often, medical devices treat such ailments and symptoms with electrical stimulation delivered to patient tissue via electrodes on one or more leads. For some conditions, the medical device also senses electrical activity within the patient via the electrodes. Based on the electrical activity, the medical device may detect a symptomatic event, and deliver stimulation to treat the event in response to the detection.
For example, many patients suffer from epilepsy, which is a condition that occurs when electrical signals in the brain are disrupted, e.g., hypersynchronized, causing a seizure. Occurring repeatedly, each seizure may cause a brief change in a patient's body movements, awareness, emotions, or senses. These seizures may affect a patient's ability to hold a job, drive a car, enjoy certain activities, or conduct other activities. Brain stimulation has been used to treat some epilepsy patients. For example, implantable medical devices have been used to electrically sense the beginning of a seizure and, if appropriate, deliver electrical stimulation to the brain to terminate the seizure. Applying stimulation in this manner may significantly increase a patient's quality of life.
A single lead may have a plurality of electrodes, and multiple conductors, each corresponding to one or more of the electrodes. The lead may be directly connected to a medical device, or may be connected to the medical device via one or more lead extensions. Conductors within a lead extension couple the conductors within a lead to the implantable medical device. An electrode, the conductors that couple the electrode to the implantable medical device, and tissue proximate to the electrode may be referred to as an electrical “path,” through which the implantable medical device may sense electrical activity within a patient and/or deliver stimulation to the patient.
Over time, the impedance of such an electrical path may change due to, for example, degradation of the lead material or tissue growth proximate to the electrode. In some cases, the insulation of a lead may fail, causing a short between two electrical paths. In other cases, a conductor may fracture. Fractures may be caused by bending, twisting, compression, or tension stresses resulting from patient movement. Fractures occur with greatest frequency when implanted leads extend subcutaneously through the neck and to the cranium of a patient, such as might be the case for brain stimulation to treat epilepsy. Shorts and fractures may be intermittent. Shorts, fractures and other electrical path impedance changes may impair the ability of a medical device to effectively treat a patient.